NOUN (2)

1. a pale yellow crystalline hydrocarbon C16H10 extracted from coal tar;

2. the small hard nutlet of a drupe or drupelet; the seed and the hard endocarp that surrounds it;

The Collaborative International Dictionary of English v.0.48:

Pyrene \Py"rene\, n. [Gr. ? fire.] (Chem.)
   One of the less volatile hydrocarbons of coal tar, obtained
   as a white crystalline substance, C16H10.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pyrene \Py"rene\, n. (Bot.)
   Same as Pyrena.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pyrene
    n 1: a pale yellow crystalline hydrocarbon C16H10 extracted from
         coal tar
    2: the small hard nutlet of a drupe or drupelet; the seed and
       the hard endocarp that surrounds it